FIGS. 1 and 2 illustrates a prior art photo pen which includes a pen body 1a, a seat 2a, a battery 3a, a push 4a and a cover 5a. The upper end of the pen body 1a is installed with a seat 2a. The top and bottom of the seat 2a are installed with a conductive pin 21a and a light emitting unit 22a. A battery 3a is installed on the conductive pin 21a. The battery 3a is installed with a push 4a. The push 4a has a spacer 41a with a through hole 411a at the center thereof so as to resist against the battery 3a. The upper side of the spacer 41a resists against a positioning plate 43a through a spring 42a. The bottom of the positioning plate 43a extrudes with a rod 431a. The periphery of the rod 431a has a conductive reed 44a extending to the through hole 411a of the spacer 41a. A movable block 45a, a press block 46a and a cap 47a are sequentially installed from the positioning plate 43a. A cover 5a covers on the battery 3a and the push 4a so that the spacer 41a of the push 4a is fixed to the inner wall of the cover 5a. At the connection of the seat 2a and the cover 5a is disposed with a ring 6a. However, in this prior art photo pen, the light from the light emitting unit 22a is only dispersed from the tip 7a. The surface of the pen body 1a will not emit light. Therefore, an advertising effect can not be present. The photo pen serves to increase the distance between the conductive reed 44a of the push 4a and the battery 3a. When the cap 47a of the photo pen is pushed to a dead point, the light emitting unit 22a lights up. And thus the operation is very inconvenient.